1. Field of the Invention
The present invention relates to a monolithic catalyst converter, and a process for producing the same.
2. Description of the Related Art
A monolithic catalyst converter includes a catalyst container connected with the pipes of an exhaust system, and a monolithic catalyst held in the container. By using the monolithic catalyst converter, exhaust gases emitted from engines can be brought into contact with the monolithic catalyst by way of an inlet pipe of the exhaust system, and thereby the monolithic catalyst can purify the harmful components involved in the exhaust gases.
There is a clamshell (or pancake) monolithic catalyst converter. The clamshell monolithic catalyst converter is manufactured in the following manner: an upper member and a lower member are formed by pressing. Both of the upper and lower members are formed like a bowl, and have a flange which is formed all around the periphery to constitute a mating surface. Then, a monolithic catalyst is held in the upper and lower members. Finally, the upper and lower members holding the monolithic catalyst therein are welded at the flanges. In the resulting clamshell monolithic catalyst converter: the upper and lower members constitute a catalyst container including a tube-shaped member, and a pair of funnel-shaped cone members; the tube-shaped member holds the monolithic catalyst support therein; and the funnel-shaped cone members have a diametrically-reduced opening which is connected with a pipe of an exhaust system.
In the clamshell monolithic catalyst converter having the catalyst container, however, the catalyst container made of the upper and lower members is likely to be distorted by thermal influences during welding, and might accordingly be damaged in terms of assembly operability with respect to the exhaust pipes of the exhaust system.
Further, in the clamshell monolithic catalyst converter, welded portions remain in the tube-shaped member of the catalyst container as bonded portions which face each other in an axial direction thereof, and they also remain in the funnel-shaped cone members as bonded portions which face each other in a radial direction thereof. The welded portions result from the welding of the upper and lower member at their flanges. Therefore, in order to securely inhibit the exhaust gases from leaking through all of the bonded portions, the clamshell monolithic catalyst converter should be inspected by a troublesome leak test whether all of the bonded portions are formed in an air-proof manner.
Furthermore, in the clamshell monolithic catalyst converter, the flow of exhaust gases is likely to be disturbed by the bonded portions in the catalyst container. The disturbed flow increases exhaust resistance, and might eventually deteriorate the output of engines. In particular, it is believed that the deterioration of engine output results mainly from the bonded portions which extend radially in the funnel-shaped cone members. On the other hand, when a tube-shaped member and a pair of cone-shaped members are prepared independently at first, and when these 3 members are welded together in a circumferential direction so as to form a catalyst container, the welded portions result in the bonded portions which extend in a circumferential direction in the tube-shaped member and the cone-shaped members. It is also believed that these circumferentially-extending bonded portions cause problems similar to those caused by the axially-extending bonded portions.
Furthermore, in the clamshell monolithic catalyst converter, the upper and lower members should be provided with a flange which is formed all around the periphery to constitute a mating surface, and should be welded together at the flanges over a long distance by expensive welding facilities. Hence, when manufacturing the clamshell monolithic catalyst converter, the material cost and the welding cost are so high that they push up the overall manufacturing cost. In addition, there is some fear that the welding might deteriorate the working environment.
Whereas, Japanese Unexamined Patent Publication (KOKAI) No. 2-264,110 proposes a monolithic catalyst converter whose catalyst container is one-piece. According to the publication, a one-piece catalyst container is manufactured in the following manner: a tube-shaped workpiece is pressed at the opposite ends to form an inlet port and upper and lower closure ends which extend outwardly from the inlet port to the opposite sides, and an outlet port and upper and lower closure ends which extend outwardly from the outlet port to the opposite sides. Thereafter, at the opposite ends of the pressed tube-shaped workpiece, all of the upper and lower closure ends are welded together to complete a one-piece catalyst container. In the resultant monolithic catalyst converter, the catalyst container is formed integrally out of a tube-shaped workpiece. Therefore, in manufacturing the monolithic catalyst converter, the welding can be carried out over a reduced length at the opposite upper and lower closure ends. Thus, it is somehow possible to reduce the manufacturing cost, and to achieve a good working environment.
However, in the monolithic catalyst converter disclosed in the publication, the welded portions, resulting from welding the opposite upper and lower closure ends, remain as bonded portions which extend in a radial direction. Thus, even the monolithic catalyst converter has been adversely affected by the thermal influences in the welding operations, and accordingly it little exhibits perfect assembly operability with respect the exhaust pipes of the exhaust system. Moreover, the following problems are believed to arise from the radially-extending bonded portions: namely; they make the air-proof inspection indispensable; and they deteriorate the output of engines. In addition, the radially-extending bonded portions cannot reduce the manufacturing cost and establish a good working environment completely.